package javaTest;

import java.util.Arrays;

public class MyStack {
    public int[] elem;
    public int usedSize;

    public MyStack(){
        this.elem=new int[10];
    }
    public void push(int val){
        if(isFull()){
            this.elem= Arrays.copyOf(elem,elem.length*2);
        }
        elem[usedSize++]=val;
    }
    public boolean isFull(){
        return usedSize==elem.length;
    }
    public int pop(){
        if(isEmpty()){
            throw new RuntimeException("栈为空");
        }
        return elem[--usedSize];
    }
    //获取栈顶元素，但不删除
    public int peek(){
        if(isEmpty()){
            throw new RuntimeException("栈为空");
        }
        return elem[usedSize-1];
    }
    public boolean isEmpty(){
        return usedSize==0;
    }
}
